This invention relates to molding molecularly oriented containers from preforms and more particularly to a method used in conditioning such preforms prior to such molding.
U.S. Pat. No. 3,754,851, describes an "in-line" system for blow molding preforms from initially extruded tubular sections, conditioning such preforms to bring them down to molecular orientation temperature and then immediately stretching and blowing them into containers. U.S. Pat. No. 3,830,893 discloses an alternative system wherein molded preforms which have been cooled to room temperature are reheated back up to orientation temperature prior to final blowing. Both systems have advantages. Regarding the latter reheat approach, this, of course, may be carried out anywhere, but if done at a satellite location remote from that where the preforms are molded and perhaps situated close to various market areas for the finished containers, one central preform molding facility can be used to supply a number of satellite container molding plants which need only be equipped with reheat and container-molding facilities rather than with preform-making facilities also. On the other hand, molding containers directly in line without first cooling all the way down to room temperature has the energy-conserving advantage of utilizing heat incorporated into the plastic during initial extrusion to develop the temperature required for orientation rather than adding it back into the plastic during reheating.
Commonly owned copending U.S. Ser. Nos. 418,075, filed Nov. 21, 1973, now U.S. Pat. No. 3,894,835 and 424,866, filed Dec. 14, 1973, now U.S. Pat. No. 3,880,301, respectively disclose temperature conditioning and preform loading systems for an in-line process. It would be desirable in an in-line system to have the flexibility of providing cool preforms to be later brought up to orientation temperature via reheating. This might be accomplished by cooling the preforms in the molds in which they are formed to some temperature low enough to avoid their sticking together when collected in bulk after ejection from the forming molds. When the preforms are blow molded, however, this can present problems in that the integral neck flash of the yet to be molecularly oriented shape must be removed which is difficult to do in an acceptable, repetitive, high speed fashion when the thermoplastic material is relatively thick and fully set, and especially is this so when it is brittle in nature and prone to crack when machined.